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Noisy return after new system install

Just got a new 3 ton Lennox XP14 to replace an older 3 ton Lennox. To get the SEER and EER up it was matched with a 3.5 ton, CBX27UH-042 air handler. I have two returns with a damper just after the main return in an attempt to draw more air from a to hot/cold Great rm. This was not a problem before with a 3 ton AH and I was able to even out the temps with the damper. Speed on the new AH has been double checked and is correct. Only other change is I went from a 20x20x1 mid grade filter, at the AH, to a 20x25x4 Honneywell MERV 11, at the AH.

With the damper wide open I have no noise problem but have a 4-5 deg temp difference from one end of the house to the other. Tech ran system with no filter and door on and still had same noise. Tried again with door off and noise went away. He is suggesting I change the 12 inch flex on a 14x14 grill to a 14 inch flex on a larger grill. Will this be enough to work? I'm wondering if I have enough area anyway. Grill area of main return is 23x13 though the duct board that leads from it is 12x20 then makes a 2' run to a 24x26x16 " box that the 12 inch flex also leads to. Flex is maybe 25' long and sits on top of attic insulation the whole way and makes a lazy S turn to the 14x14 grill. If 14 inch flex is enough what size grill should I get 14x?

House is 1800 sq. ft. and the Great rm has a 16' cathedral ceiling and two sky lights that face WNW.

The 14"x14" grille is designed for 392 cfm. The 12" flex is good for 500 cfm. The 22"x12" grille is designed for 528 cfm. Your system needs at least 1,200 cfm.

If you go with the 14" flex the grille should be enlarged to a 20"x20" or 22"x22" (800 ccm). F.Y.I. 2 cfm per sq. in.

This work (that was needed) should have been seen during the bidding process. You should not have to pay for a poorly designed (new) system. Example: If you had a new roof installed and it leaked because it wasn't installed correctly and the salesman said, "Oh, we'll fix it, but it'll cost you extra", what would you say? Hell no!!!!............(probably).

The 14"x14" grille is designed for 392 cfm. The 12" flex is good for 500 cfm. The 22"x12" grille is designed for 528 cfm. Your system needs at least 1,200 cfm.

If you go with the 14" flex the grille should be enlarged to a 20"x20" or 22"x22" (800 ccm). F.Y.I. 2 cfm per sq. in.

This work (that was needed) should have been seen during the bidding process. You should not have to pay for a poorly designed (new) system. Example: If you had a new roof installed and it leaked because it wasn't installed correctly and the salesman said, "Oh, we'll fix it, but it'll cost you extra", what would you say? Hell no!!!!............(probably).

How do people know this? Sadly as we all know, builders don't pay for quality. My question is why are the people that do the installing do such bad work. Anything that has my name on it has quality with it.

How do people know this? Sadly as we all know, builders don't pay for quality. My question is why are the people that do the installing do such bad work. Anything that has my name on it has quality with it.

I would hope that a quality/knowledgeable minded salesman would have used the restricted return to his advantage during the sales call. You need to keep your cards to your chest until the homeowner has collected all of his bids.

The 14"x14" grille is designed for 392 cfm. The 12" flex is good for 500 cfm. The 22"x12" grille is designed for 528 cfm. Your system needs at least 1,200 cfm.

If you go with the 14" flex the grille should be enlarged to a 20"x20" or 22"x22" (800 ccm). F.Y.I. 2 cfm per sq. in.

This work (that was needed) should have been seen during the bidding process. You should not have to pay for a poorly designed (new) system. Example: If you had a new roof installed and it leaked because it wasn't installed correctly and the salesman said, "Oh, we'll fix it, but it'll cost you extra", what would you say? Hell no!!!!............(probably).

The Op was not charged for that duct work alteration. So he should pay for it to be done. The same as he would have if the salesman would have seen it, and added money to the quote for it.

The Op was not charged for that duct work alteration. So he should pay for it to be done. The same as he would have if the salesman would have seen it, and added money to the quote for it.

I guess my point was: Why wasn't that important issue addressed at the time? There are a few reasons that come to mind. First, the salesman didn't take the time or care. Second, the salesman doesn't have the knowledge. Third, the salesman's thinking was, "we can charge more to come back later and fix it".

My philosophy was: Do the job right the first time to eliminate call backs and to keep the customer happy without excuses.

however,
MANY systems are simple like for like change outs. and ductwork is not addressed.
it is a larger air handler, but the air is reduced to the same 3 tons it was before.
if it's not adequate, it's a problem that needs to be billed for. now if it was new ductwork WITH the new air handler and it's inadequate, then no, it should not be charged for fixing.

The TRUE highest cost system is the system not installed properly...
The three big summer hearththrobs...
Mel Gibson
Dwane Johnson
The A/C repairman

I guess my point was: Why wasn't that important issue addressed at the time? There are a few reasons that come to mind. First, the salesman didn't take the time or care. Second, the salesman doesn't have the knowledge. Third, the salesman's thinking was, "we can charge more to come back later and fix it".

My philosophy was: Do the job right the first time to eliminate call backs and to keep the customer happy without excuses.

I only read what the OP posted. I don't know what the contractor has to say about it. I won't condemn either, cause I wasn't there for any of the job discussions.

Get egg crate grills. expensive but no restriction. Which = no noise. Pull flex duct TIGHT!!! no skin friction!

Do you have a box (Plenum or return box) opposite the return grill or is the duct just panned out to the thickness of the wall stud? When you go to change the filter how far away from the grill is the collar for the duct? 4"?

To be fair, one of the 5 contractors I had out said I needed larger returns and suggested I enlarge both of the existing ones, which his bid included, or enlarge one and add a 3rd. One other contractor, who 3 yrs ago was here for another reason, told me then I needed a larger return, now when asked looked at the return sizes and said they were ok. I mentioned this to a 3rd contractor and he said they were ok. I asked one to give me a price for a 14" flex, to replace the 12", and a larger grill. He Quoted me X, when done with the system but I ended up using another contractor. Now the contractor I used is asking 3X to do the same thing. Have called another and got a quote of 2X.

To be fair, one of the 5 contractors I had out said I needed larger returns and suggested I enlarge both of the existing ones, which his bid included, or enlarge one and add a 3rd. One other contractor, who 3 yrs ago was here for another reason, told me then I needed a larger return, now when asked looked at the return sizes and said they were ok. I mentioned this to a 3rd contractor and he said they were ok. I asked one to give me a price for a 14" flex, to replace the 12", and a larger grill. He Quoted me X, when done with the system but I ended up using another contractor. Now the contractor I used is asking 3X to do the same thing. Have called another and got a quote of 2X.

Compared to the bid that was going to do the job right from the start and the lower bid, that you'll now have an additional expense, will you be spending more money?

Found a page for "Rules of thumb for duct systems". Here is my idea for a cheap and easy fix? Which is what the X price from above was for. Replace 12" flex (<= 510 cfm) and 14x14 grill (<= 446 cfm) with 14" flex (<=755 cfm) and a 14x24 grill (<=758 cfm). This in conjunction with the "main return" in the hall, which is limited by it's 12x20 id duct bd to 544 cfm? would add up tp 1299 cfm. As this is going into my rather large and open great rm (19x28) with the Kitchen cutting into one corner, as an alternative to the one large grill I would consider putting a wye connector in the 14" with two 12" flex leading to two 14" grills. The current 14x14 return is in the small end of the great room and a second 14x14, if used, would be around the corner 5' away facing the main part of the rm. The disadvantage to the 14x24 grill is that the bottom of it is 9' above the floor, so with it's added height I'd be sucking up all the hot air near the top of the 16' ceiling.